Reflex converter circuit



g" 1945; I K. SEILER 313 2,383,345

REFLEX CONVERTER CIRCUIT Filed 'Sep'fi. 15, 1942 Snuenloi f l nardPatented Aug. 21, 1945 oFFlcE REFLEXCONVERTER CIRCUIT i Delaware i KarlSeiler, 3rd, Jenkintown, Pa., assignorto Radio Corporation of ;America,a;corporation a Application September 15, 1942, Serial No. 458,432

r a 1 Ill-Claims. (oi. 250) This invention is concerned with an improve-,ment; in radio receivers of the superheterodyne tyamsQarid moreparticularly with a reflex converter cuit which combines the function ofafirst del tor, oscillator, and first intermediate frequencyInthepresent state ,of theflart it is known to use in superheterodynecircuits'a multifelectrode type of tube designed toperformsimultaneously the functions of a first detector and anoscillator.

lhesecorhbined; tunctions are frequently referre tofas frequencyconversion. According to my invention the saline or equivalent multieetrode tube is made to periorm in addition the function of intermediatefrequency amplification.

Asia result necessity for the use of a separate tube 2-15 circuit f orperforming the combined functions of detector-oscillator andintermediate fret quency amplifier, utilizing an electron dischargehaving'tvi'thina common envelope electrodes triode and other electrodes0011-;

heated; to the; signal grid electrode of the heptodefthe triodeelectrodes having circuit elements connected thereto to constitute'agenerator of i ea oscillations which are injected into the searchstream'of the heptodeptheoutput of the heptoiieincluding' anintermediate frequ'encyfcin f cui t hetweedwhich cincuit and the signalgrid 1 e ctrode of theheptode afeed back circuit is confn ted forthepurposeor reliexing and amplify- ;i said intermediate frequencyenergy.

Other objects of the invention are to provide a co Qe'rt circuit whichWdflld The attractive in o I rice receiving sets wherethe cost must writo a to provide a receiver of educed sizeandweight; andin battery-operaits a; prevm e e nonne r perauon by reprovide in a superheterodynereceiver, a

atteryconsumption. In' single frequency.

the following description takenin connection with the accompanyingdrawing in which the single figure illustrates a preferred convertercircuitembodying the present invention of combined first detector,oscillator and intermediate frequency stages.

In the circuit of the accompanying drawing the tube designated V is amulti-electro-de' vacuum tube and may *be of the typeknown as 6J8-G, oroneequivalent thereto. This tube,also'known as a triode-heptodeconverter,yc0ntains a triode section anda heptode section within thesame evacuated envelope, an indirectly heated cathode K ibeing common totooth. The heptode section comprises the cathode K, "an output or plateelectrode P and a plurality of grid G1 to G5 interposed inthe spacebetween K and P in the order named. The triode section comprises theoathode K, grid Go and plate P0." In the normal'use or this tulbeas aconverter, the cathode K, first grid Goan'd plate P0 constituting thetriode section have external circuit elements connected thereto toperIorm the function or a local oscillator for generating the localoscillations, the grid G0 serving as the output electrodeoftheoscillator. The signal oscillations are impressed on the grid G1 ofthe heptode section and'the locally produced oscillations are injectedinto theelectron stream ibetween cathode K and {plate P by way of thegrid G3 which has a direct connection to the oscillator "grid Go Withinthe tube. Du to the mixing action withinthetube, oscillations ofintermediate frequency appear in the output circuit connected to theplate P. The second and I'Ourth'-gridsGz, G4 re connected togetherinside the tube envelope, have a positive potential impressed thereon,and serve to accelenate the electron stream and to shieldelectrostaticallythe signal control grid G1 from voltage fluctuations ontheinjector grid G and on the plate P. Grid Gals the usual suppressorgrid having an internal connection to the cathode K.

The use ofjthe above or equivalent tube and the circuit connectionstherefore in accordance with the present invention will now be pointedout more particularly. The grid Gi serves as the signal control grid andhas connected between it and the cathode K the input circuit L1C1 whichis tuned to the received incoming signal oscillations. If desiredanREamplifier stage may precede the detector-oscillator-I.F, amplifier tubeV,the same being interposed lbetw-een the antenna A and aidre'sonahtcircuit Iii- 0; through the radio frequency transformer T1.-

The gr id G3 being directly connected to at triode grid Go derivestherefrom the oscillations generated by the triode section, theelectrodes of which have connected thereto external circuit 1 elementsto constitute the local oscillator of the R1 and C7 are respectively theusual grid-leak and grid-condenser employed in oscillators of this type.Voltage for plate P is applied from a suitable power supply sourceindicated by +B+. Voltage for the plate P is applied from said sourcethrough a voltage dropping resistor R2 andtha't for screen grids G2-'Giis applied through'a dropping resistor R3. C8 is a screen grid bypasscondenser. j i

In order to provide suitable operating bias for thesignal control gridGrand oscillator grid Go, the cathodeK has connected between it andground the conventional self-biasing resistancecapacit'y network, R4'C4. In the event that it is desired to provide the receiver withautomatic volume control, the AVG control bias may be obtained in theusual manner from the second detector and fed either to .the signal gridG1 or to the injector 'grid G3, or both.

The variable tuning condensers C1 and C2, and theyariable' condenser 03of the R. F. amplifier, if oneis used, are mechanically interconnectedas sho'wnby'the, dotted line U for the purpose ofpr'oviding uni-control.j As is wellknown, by reason of the interaction between thereceivedsignals impressed on grid G1 and the locally generatedoscillations injected on grid G3 there Willbe developed'in the fixedtuned circuit I1 connected to the plate P oscillations of theintermediate frequency (I. F.)'. Coupled to the circuit I1 is a secondfixed tuned circuit I2 alsoresonant to the intermediate frequencyoscillations, the coils of said circuits constituting the transformerT2. The oscillations occurring in the circuit I2 may then be furtheramplified in a second intermediate frequency stageor else fed directlyto a second detector, the resulting audio currents being fed to an audiofrequency amplifier and reproduced by a loudspeaker in the usual manner,the'latter elements not being shown.

In order that the frequency converter above described may assume theadditional function of an amplifier of the resulting intermediatefrequency, the latter frequency (sum or difference) developed in theplate circuit of the combined converter oscillator tube V is fed formaximum gain back onto the signal control grid G1 by way of the feedbackloop FB which includes the filter network in the "form of I. F.transformer T2 and series-connected condenser C9 and resistor R9 so thatonly the difference (or sum) frequency is' fed back, the original'andthe unwanted sum (or difference) of the original frequencies beingsuppressed by the I. F. transformer tuned circuit acting as a-band'passfilter for only the difference (or sum) frequency in the heptode plate"circuit. This arrangement is most advantageous in applications-where theintermediate frequency is considerably removed from the tuning rangefrequencies and oscillator frequency because locki in of theintermediate and signal frequencies in I the I. F. transformer wouldoccur were the difphase reversal through the tube itself and anadditional 180 phase reversal through the condenser C9 inthe feedbackloop since when one plate of this condenser is positive the other issimultaneously negative and therefore adequate amplification of thesignal can under these conditions take place. H The gain that can berealized from thearrangement is limited because if a considerable amountof intermediate frequency is fed back, the circuit will oscillate, hencethe reason for the se'rie sresistor R9 in the feed back loop. With aconverter tube of the type having a high conversion conductance maximumgain will be obtained."

'While'I'haVe shown and described only'one preferred embodiment of theinvention; it will be understood that "modifications and changes may bemade without departing from the spirit and scope of the invention, aswill be understood by those skilled in the art.

WhatIclaimisz v j 1. In a superheterodyne receiver, a circuit forperforming the combined functions of firstdetector-oscilla'tor andintermediatefrequency amplifier, comprising an'electron discharge tubehaving within a common'envelope a cathode, a pluralityofgridelectrodesand a pair of anode electrodes; a tuned input circuit having im-*pressed thereon the received signal oscillations connected betweencathode and one of "the grid electrodes, external circuit'elements'connected betweena second grid electrodasaid cathode and one of theanode electrodes to serve as a generator of local oscillations, anintermediate frequency circuit connected to *the'second anode electrodeandhaving an output terminalgand-a circuit forfeeding back some of theintermediate frequency energy for amplification bysaid tube, saidcircuitbeing connected between the output terminal of theintermediate frequencycircuit and the grid electrode towhich the tunedinput circuit isconnected; 2. In a superheterodyne receiver, a circuit for performingthe combined functions of first detector-oscillatorand intermediatefrequency amplifier, comprising 'an' electron discharge tube havingwithin a common envelope a cathode, a plurality of gridelectrodes'andapair-of anode electrodes, a tuned input circuit'havingimpressed thereon the received signal oscillations connected betweencathode and one of the grid-electrodes,

external circuit elements connected between a cuit conncted to thesecond anodeelectrodeand having an output terminaL-and' a circuit forfeed me back some of the interme'diatefrequency energy for amplificationbysaid tube, said circuit including a series resistor-capacitor networkconnected between the output terminal of the intermediate frequencycircuit and the gridelectrode to which the tunedinput circuit isconnected.

3. A combined first detector-oscillator anamtermediate frequencyamplifier circuit, comprising an electron discharge tube having with-in:a common envelope a cathode, a pluralityor grid.

I electrodes and an output anode electrode, a tuned 'input circuithaving impressed thereon the re- I ceived signal oscillations connectedbetween cathode and one of the grid electrodes, external tween thereceived and local oscillations con- I nected to the output anodeelectrode, a second circuit tuned to the intermediate frequencyoscillations coupled to thefirst intermediate frequency circuit, andmeans for feeding back to the signal grid; in phase with the receivedsignal oscillations the intermediate frequency oscillations derived fromsaid second circuit for further amplification by said discharge tube.

4. A circuit asdefined in claim 3 wherein the feedback means comprises acircuit including series connected resistance and capacity con- 3 nectedbetween the second intermediate frequency I circuit and the signal inputgrid.

5. In a superheterodyne receiver, a circuit for performing the combinedfunctions of first detector-oscillatorand intermediate frequencyampllfier, comprising an electron discharge tube having within acommonenvelope electrodes constituting a triode and other electrodesconstituting a heptode, the triode and heptode having a common cathode atuned input circuit having impressed thereon the receivedsignaloscillations connected to the signal grid electrode of theheptode, circuit elements connected to the triode 'electrodesconstituting a generator of local oscillations, means for injecting saidlocal oscillations into the electron streamlof the heptode, anintermediate frequency circuit connected to the output of the heptode,and a feedback circuit connected betweensaid intermediate frequencycircuit and 1 the signal grid electrode of the heptode whereby it saidintermediate frequency energy is amplified by the heptode portion of thetube.

16. A circuit as defined in claim 5 wherein the feedback circuitincludes a resistor and a condenser connected in series.

I 7. In a superheterodyne receiver, a circuit for performing thecombined functions of first detector-oscillator and intermediatefrequency amplifier, comprising an electron discharge tube having withina common envelope electrodes constituting a triode and other electrodesconstituting a heptode, the triode and heptode having a common cathode,a tuned input circuit having impressed thereon the received signaloscillations connected to the signal grid electrode of the heptode,circuit elements connected tothe triode electrodes constituting agenerator of local oscillations, means for injecting said localoscillations into the electron stream of the heptode, a bandpass filternetwork which transmits only the intermediate frequency resulting fromthe frequency conversion connected to the output of the heptode, and afeedback circuit connected between said filter network and the signalgrid electrode of the heptode whereby said intermediate frequency energyis amplified by the heptode portion of the tube. l

8. A combined frequency converter-intermediate frequency amplifier stageutilizing a tube having a plurality of electrodes, comprising a i tunedinput circuit on which the received signal output to the input of saidstage for feeding back some of the intermediate frequency energy to beamplified by said stage.

9. A combined frequency converter-intermediate frequency amplifier stageas defined in claim 8 wherein the feed back circuit includes a resistorand a condenser connected in series.

10. In a superheterodyne receiver, a circuit for performing the combinedfunctions of first detector-oscillator and intermediate frequencyamplifier, comprising an electron discharge tube having within a commonenvelope, cathode, grid and anode electrodes which constitute a triode,and a cathode, an anode and a plurality of interposed grids whichconstitute a heptode, said grids including a signal grid and a mixergrid, said cathode being common to said triode and heptode, a tunedinput circuit having impressed thereon received signal oscillationsconnected to the signal grid electrode of the heptode, circuit elementsconnected to the triode electrodes constituting a generator of localoscillations, a connection between the grid of the triode oscillator andthe mixer grid of the heptode for injecting the local oscillations intothe electron stream of,

